Digital broadcast receiving apparatus

ABSTRACT

A digital broadcast receiving apparatus, which has a receiving circuit for receiving a transmitted high frequency signal of a plurality of time division multiplexed programs, includes a circuit for selecting a better receiving characteristic condition while a desired program is not received.

This Application is a U.S. National phase Application of PCTINTERNATIONAL APPLICATION PCT/JP2004/003393.

TECHNICAL FIELD

The invention relates to a digital broadcasting receiving apparatus forreceiving a transmitted signal of a plurality of time divisionmultiplexed programs, particularly, a digital broadcast receivingapparatus, which is effective when it is used for mobile terminals.

BACKGROUND ART

FIG. 5 is a block diagram of a conventional digital broadcast receivingapparatus in mobile terminals. FIGS. 6A and 6B illustrate a relationbetween a time division multiplexed program and power supply controllingtiming in a conventional digital broadcast receiving apparatus.

A conventional digital broadcast receiving apparatus includes antennaportion 1602, receiving circuit 1142, power supplying circuit 1143 anddemodulating portion 1141.

Antenna portion 1602 receives at antenna 1601 a radio wave in a space toconvert the radio wave into an RF receiving circuit input signal at BPF(a bandpass filter) 1104.

Receiving circuit 1142 consists of channel-selecting portion 1109 andother portions. Channel-selecting portion 1109 includes VCO (voltagecontrolled oscillator) 1106, synthesizer 1107 and controlling voltagegenerating circuit 1108. Portions of receiving circuit 1142 other thanchannel-selecting portion 1109 include RF variable gain amplifier 1110,frequency converting circuits 1111 and 1113, 90° phase shift circuit1112, low pass filters 1114 and 1115, frequency adjusting circuit 116and base band variable gain amplifiers 1117 and 1118. Receiving circuit1142 selects a desired channel signal from inputted signals and convertsthe selected signal into a base band signal.

Demodulating portion 141 demodulates the base band signal to output atransport stream (referred to as a TS, hereinafter).

Power supplying circuit portion 1143 supplies receiving circuit 1142 anddemodulating portion 1141 with power.

FIG. 6A shows time division multiplexing of digital broadcasttransmitted after time division multiplexing. In FIG. 6A, signals fromProgram 1 to Program 4 are time multiplexed.

Signal information recover circuit 126 of demodulating portion 1141obtains program timing from Program 1 to Program 4 on the basis of theTS. In the case that Program 3 is desired, for example, a timing signalshown in FIG. 6B is outputted. Power supply on/off timing generatingcircuit 1134 uses the timing signal to generate a signal whose voltagelevel is capable of on/off control of power supplying circuit 1137 ofreceiving circuit 1142 other than channel-selecting portion 1109. Asdescribed above, turning off during an undesired program of the TS asupplying power source to receiving circuit 1142 other thanchannel-selecting portion 1109 in which it takes long time to becomestable after turning on the power supply allows a low consumption powerto be enabled and battery consumption to be restrained.

As information of former art references concerning to the invention, USLaid-Open Patent Application No. 2002-015941 A1 is known, for example.

The digital broadcast receiving apparatus to be used, which is built ina mobile terminal, is, however, used as a mobile, so that a receivingpoint is changed. Accordingly, a state of a radio wave changes as timepasses, and therefore, a stable reception is impossible. Nevertheless,changing the state of digital broadcast receiving apparatus always inaccordance with a state of the radio wave causes a problem that it takeslong time until the circuit becomes steady, and thereby, an image or asound would be interrupted.

Furthermore, a digital broadcast receiving apparatus described inJP-A-2001-7713 is disclosed as follows.

A signal level of each analog broadcast channel is stored in advance aschannel information in a channel information memory portion. Inchannel-selecting of a desired channel, an analog broadcast wave signalof a channel close to the desired channel is acquired from the memoryportion. An operation starting point is set high to increase strengthagainst a interference wave in the case that the interference wave is ata high level while the operation starting point is set low to cover adynamic range in the case of no interference wave.

This enables, regardless of existence of a high interference wave havinga high signal level in a close channel, the digital broadcast in adesired channel to be stably received while a low noise characteristicis kept.

The digital broadcast receiving apparatus to be used, which is built ina mobile terminal, is, however, also used as a mobile, so that areceiving point is changed as time passes. Therefore, the operationstarting point should be also switched as time passes since a level ofthe interference wave also varies. This causes a problem that a signalis interrupted in switching the operation starting point.

DISCLOSURE OF THE INVENTION

An object of the invention is to provide a digital broadcast receivingapparatus capable of stable receiving without interruption of an imageor a sound even in the case of use as a mobile.

A digital broadcast receiving apparatus according to the inventionincludes a receiving circuit for receiving a transmitted high frequencysignal of a plurality of time division multiplexed programs and acircuit for selecting a condition of a better receiving characteristicduring a period in which a desired program is not received.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a digital broadcast receiving apparatusaccording to Embodiment 1 of the invention.

FIGS. 2A to 2E illustrate timing of an integral signal of a digitalbroadcast receiving apparatus according to Embodiment 1 of theinvention.

FIG. 3 is a flowchart illustrating a digital broadcast receivingapparatus according to Embodiment 1 of the invention.

FIG. 4 is a block diagram of another digital broadcast receivingapparatus according to Embodiment 1 of the invention.

FIG. 5 is a block diagram of a conventional digital broadcast receivingapparatus.

FIGS. 6A and 6B illustrate an operation of a conventional digitalbroadcast receiving apparatus.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

An embodiment of the invention will be described below, made referenceto the drawings.

FIG. 1 is a block diagram of a digital broadcast receiving apparatusaccording to an embodiment of the invention. FIGS. 2A to 2D illustratetiming of an integral part signal of the digital broadcast receivingapparatus. FIG. 3 is a flowchart illustrating an operation of thedigital broadcast receiving apparatus.

In FIG. 1, a transmitted high frequency signal of a plurality of timedivision multiplexed programs is inputted to antenna potion 105. Antennaportion 105 includes horizontally polarized wave antenna 101, verticallypolarized wave antenna 102, antenna switching circuit 103 and bandpassfilter 104 capable of varying a passband (referred to as BPF,hereinafter).

Station-selecting portion 109 includes voltage controlled oscillator 106(referred to as VCO, hereinafter), synthesizer 107 and controllingvoltage generating circuit 108 for controlling a passband of BPF 104 inaccordance with a received channel.

Receiving circuit 142 includes RF variable gain amplifier 110, frequencyconverting circuits 111 and 113, phase shift circuit 112, low passfilters (referred to as LPF, hereinafter) 114 and 115, base bandvariable gain amplifiers 117 and 118 and channel-selecting portion 109.

RF variable gain amplifier 110 controls amplitude of an outputted signalfrom BPF 104. An outputted signal from VCO 106 is inputted to phaseshift circuit 112, which supplies frequency converting circuits 111 and113 with a signal having phase difference of 90 degrees. Frequencyconverting circuit 111 converts an output from RF variable gainamplifier 110 into a baseband I signal. Frequency converting circuit 113converts an output from amplification circuit 110 into a base band Qsignal. LPFs 114 and 115 limit bandwidth of outputted signals fromfrequency converting circuits 111 and 113, respectively. Each of baseband variable gain amplifiers 117 and 118 controls amplitude of outputsignals from LPFs 114 and 115, respectively.

Power supply portion 144 includes battery 136 and power supplyingcircuits 137, 138 and 139 for converting a voltage of battery 136 into apredetermined voltage. Power supplying circuit 137 supplies receivingcircuit 142 other than channel-selecting portion 109 with a voltage.Power supplying circuit 138 generates a voltage to be supplied todemodulating portion 141. Power supplying circuit 139 generates avoltage to be supplied to channel-selecting portion 109.

In demodulating portion 141, outputs from base band variable gainamplifiers 117 and 118 are converted into digital signals respectivelyby means of AD converters 121 and 122. Outputs from AD converters 121and 122 are orthogonally demodulated by means of orthogonallydemodulating circuit 123 and are FFT-detected by means of FFT detectingcircuit 124. An output from FFT detecting circuit 124 undergoes an errorcorrecting process in error correcting circuit 125 (referred to as FEC,hereinafter) to output TS signal 130. Signal information recover circuit126 outputs a signal shown in FIG. 2B on the basis of TS signal 130 tocontrol power supplying circuit 137 through power supply on/off timinggenerating circuit 134. That is to say, timing generating circuit 134turns on and off a power supply of a part of receiving circuit 142 otherthan channel-selecting portion 109. Signal information recover circuit126 outputs a signal shown in FIG. 2E to parameter switch timinggenerating circuit 133.

Level detecting circuit 127 compares output amplitude of orthogonallydemodulating circuit 123 with reference value amplitude to output asignal to RFAGC controlling portion 132 and BBAGC controlling portion131 in accordance with a result of the comparison. RFAGC controllingportion 132 controls a gain of RF variable gain amplifier 110 whileBBAGC controlling portion 131 controls a gain of base band variable gainamplifiers 117 and 118, on the basis of an output from level detectingcircuit 127 so that an input signal level of AD converters 121 and 122would be constant.

Operation starting point controlling signal 129 controls RFAGCcontrolling portion 132 directly and BBAGC controlling portion 131through RFAGC controlling portion 132. That is to say, operationstarting point controlling signal 129 can control operation startingpoints of RF variable amplifier 110 and base band variable gainamplifiers 117 and 118.

In such gain adjustment for making an input level of AD converters 121and 122 constant, a rate between a gain of RF variable gain amplifier110 and a gain control amount of base band variable gain amplifiers 117and 118 can be changed as follows.

Operation starting controlling signal 129 can change an operationstarting point of RF variable gain amplifier 110 by adding a DC offsetto an output signal of RFAGC controlling portion 132. Setting anoperation point so as to start operation from weak power, for example,allows a gain of RF variable gain amplifier 110 to be small. Operationstarting point controlling signal 129 thus adds a DC offset enlarging again of base band variable gain amplifiers 117 and 118 in BBAGCcontrolling portion 131. As a result, a rate of a gain control amountcan be changed while input levels of AD converters 121 and 122 are keptto be constant. Similarly, in the case of setting an operation point soas to start operation from strong power, a gain of RF variable gainamplifier 110 can be made large. Operation starting point controllingsignal 129 thus adds a DC offset, which makes a gain of base bandvariable gain amplifiers 117 and 118 small in BBAGC controlling portion131. As a result, a rate of a gain controlling amount can be changedwhile input levels of AD converters 121 and 122 art kept to be constant.

Parameter switch timing generating circuit 133 switches betweenhorizontally polarized wave antenna 101 and vertically polarized waveantenna 102 through antenna switching circuit 103 on the basis of signalC from electric field strength detecting circuit 145 and signal E fromsignal information recover circuit 126.

As shown in FIGS. 2A to 2D, signal A transmitted to antennas 101 and 102is obtained by time division multiplexing four programs (Program 1 toProgram 4), for example. Power supply on/off timing generating circuit134 controls on and off of power supplying circuit 137 on the basis ofcontrolling signal B shown in FIG. 2B. That is to say, power supplyingcircuit 137 is turned on when signal B is at a high level and a voltageis supplied to receiving circuit 142 other than channel-selectingportion 109. When a desired program is Program 3, for example,controlling signal B reaches a high level in Program 2, which has beenmultiplexed just before Program 3, and reaches a low level in the timingat which Program 3 is completed.

Lowering of consumption power of a digital broadcast receiving apparatusis performed as described above. The electric field strength detectingcircuit detects electric field strength on the basis of outputs fromBBAGC controlling portion 131 and the RFAGC controlling portion, namely,a signal for controlling gains of amplification circuit 110 andamplification circuits 117 and 118. Electric field strength detectingcircuit 145 outputs output signal C shown in FIG. 2C. That is to say,signal C indicates input electric field strength to receiving circuit142. Signal E shown in FIG. 2E is outputted from signal informationrecover circuit 126 and inputted to parameter switch timing generatingcircuit 133. Signal E is at a high level when signal B is at a highlevel and during a period in which signal A is in Program 2.

Switch of the antennas is allowed during a period in which signal E isat a high level. Signal D shown in FIG. 2D is an output from parameterswitch timing generating circuit 133. Switching circuit 103 selectshorizontally polarized wave antenna 101 when signal D is at a low leveland vertically polarized wave antenna 102 when signal D is at a highlevel.

Next, operations of parameter switch timing generating circuit 133 andelectric field strength detecting circuit 145 will be described.Electric field strength detecting circuit 145 operates while signal B isat a high level and detects the electric field strength of an electricwave received at antenna portion 105. Timing generating circuit 133first obtains electric field strength EFI-1, which is detected bydetecting circuit 145, while signal E is at a high level. Afterobtaining EFI-1, timing generating circuit 133 inverts its output signallevel so as to switch an antenna currently selected by switching circuit103 (antenna 101, for example) to another antenna (antenna 102, forexample). Timing generating circuit 133 obtains electric field strengthEFI-2 from detecting circuit 145 after switching circuit 103 selects theother antenna (antenna 102). In the case that EFI-2 is smaller thanEFI-1, timing generating circuit 133 inverts its output signal levelagain so as to select an original antenna (antenna 101), which had beenselected before switching. On the other hand, timing generating circuit133 maintains its output signal level when EFI-2 is larger than EFI-1.

Control of power supplying circuit 137 and switch between horizontallypolarized wave antenna 101 and vertically polarized wave antenna 102 bymeans of antenna switching circuit 103 will be described, made referenceto a flowchart shown in FIG. 3.

First, a power supply for whole receiving circuit 142 is turned on atStep 300. Horizontally polarized wave antenna 101 is then selected atStep 301 to select a desired channel in Step 302. That is to say,channel-selecting signal S is used for setting an output frequency fromchannel-selecting portion 109 (frequency of VCO 106) and passingfrequency of BPF 104.

Then, electric field strength <1> is detected by electric field strengthdetecting circuit 145 at Step 303 and an antenna is switched tovertically polarized wave antenna 102 at Step 304 following to Step 303.At Step 305, electric field strength <2> is detected. When it is foundat Step 306 that electric field strength <1> is larger than electricfield strength <2>, horizontally polarized wave antenna 101 is set atStep 307.

When an output signal from power supply on/off timing generating circuit134, namely, output signal B of a signal information recover circuitreaches a low level at Step 308 after Step 307, power supplying circuit137 is turned off at Step 309.

Then, after signal B reaches a high level at Step 310, power supplyingcircuit 137 is turned on at Step 311 to detect electric field strength<5>.

At Step 313, an antenna is switched to vertically polarized wave antenna102 and electric field strength <6> is measured at Step 314. When it isfound that electric field strength <5> is larger than electric fieldstrength <6> at Step 315, the routine returns to Step 307.

When it is found that electric field strength <5> is smaller thanelectric field strength <6> at Step 315, the routine goes to Step 317.In the case that signal B reaches a low level at Step 317, powersupplying circuit 137 is turned off at Step 318. Then, when signal Breaches a high level at Step 319, power supplying circuit 137 is turnedon at Step 320. After electric field strength <3> is measured at step321, horizontally polarized wave antenna 101 is selected at Step 322. AtStep 323, electric field strength <4> is measured. When it is found inStep 324 that electric field strength <3> is larger than electric fieldstrength <4>, vertically polarized wave antenna 102 is selected at Step316 and the routine goes to Step 317. In the case that it is found inStep 324 that electric field strength <3> is smaller than electric fieldstrength <4>, the routine goes to Step 308. When it is found in Step 306that electric field strength <1> is smaller than electric field strength<2>, the routine goes to Step 317.

As described above, switching is performed between horizontallypolarized wave antenna 101 and vertically polarized wave antenna 102during an undesired receiving program to select a state in which anelectric field inputted to receiving circuit 142 is strong, that is, astate having a receiving characteristic. Accordingly, a desiredreceiving program can be received with high performance, andfurthermore, a signal is not interrupted since switching is not carriedout in receiving a desired program.

FIG. 4 is a block diagram in which an antenna switching function iseliminated from and error ratio measuring circuit 150 is added to adigital broadcast receiving apparatus according to an embodiment of theinvention shown in FIG. 1. In FIG. 4, a component having the samefunction to that of FIG. 1 is marked with the same reference number. InFIG. 4, an antenna switching function, namely, vertically polarized waveantenna 102, a switching circuit 103 and parameter switch timinggenerating circuit 133 may be provided, similarly to FIG. 1.

Error ratio measuring circuit 150 measures a packet error ratio tooutput signal F indicating whether or not the measured value is largerthan a predetermined value. While an undesired program is received andpower supply of receiving circuit 142 is on (while signal E shown inFIG. 2E is at a high level), carried are following operations. In thecase that signal F indicates a packet error ratio worse than thepredetermined value even when output C of electric field strengthdetecting circuit 145 indicates electric field strength large enough, itis judged that a high interference wave exists in the vicinity.Operation starting point controlling circuit 135 then adds a DC offsetto an output signal of RFAGC controlling portion 132 in order toincrease strength against a interference wave so that an operation pointwould be set to start operation from weak power. As a result, a gain ofRF variable gain amplifier 110 becomes small, so that an input level offrequency converting circuits 111 and 113 are decreased. Accordingly, alevel of distortion is lowered and this allows an error ratio to beimproved.

Operation starting point controlling circuit 135 changes an operationstarting point in accordance with signals F and C, with reference totiming of signal E, so that the operation starting point is not changedin receiving a desired program, and therefore, a signal is notinterrupted.

In the embodiment of the invention, existence of an analog broadcastwave signal of a channel close to a desired channel is judged on thebasis of the error ratio and the electric field strength of the desiredchannel. Directly measuring a signal level of an analog broadcast wavesignal of a close channel, however, allows a similar result to beobtained. Further, an adjacent signal is analog broadcast wave signal inthe embodiment, but a similar effect can be obtained even in the case ofa digital broadcast wave signal or other undesired signals.

In the description from FIG. 2A to FIG. 2D, comparison of receivingconditions is carried out every cycle during an undesired signal with aparameter (an antenna characteristic or an operation point of a variablegain adjusting circuit) changed. In the case that the change of thereceiving condition is considered not to be fast, however, a similarresult can be obtained even when the comparison of receiving conditionsis carried out once per several cycles or even when the comparison isperformed during an undesired signal with a parameter changed only inthe case that degradation of receiving performance reaches apredetermined value in receiving a desired signal so as to select thecondition with the better receiving performance.

INDUSTRIAL APPLICABILITY

As described above, in accordance with the invention, a parameter suchas an antenna characteristic or an operation staring point of a variablegain controlling circuit is switched during an undesired receivingprogram to select an optimum parameter, so that a desired receivingprogram can be received with high performance and a signal is notinterrupted since the switch is not performed in receiving a desiredprogram. Furthermore, a power supply of an unnecessary circuit can beturned off while a circuit of an undesired program is not in use. Thisallows a low consumption power effect to be maintained.

1. A digital broadcasting receiving apparatus, having a receivingcircuit for receiving a transmitted high frequency selected programsignal of a plurality of time division multiplexed programs, comprising:an electric field strength detector for detecting the strength of anelectric field; an error ratio measuring circuit for measuring errors inreceived data packets; a radio frequency variable gain circuit having aradio frequency operation starting point, the radio frequency operationstarting point determining a radio frequency power level of the radiofrequency variable gain circuit; a baseband variable gain circuit havinga baseband operation starting point, the baseband operation startingpoint determining a baseband power level of the baseband variable gaincircuit; an operation starting point controlling circuit that varies: a)the radio frequency operation starting point to start operation from alow radio frequency power level which is lower than a high radiofrequency power level used when detecting the electric field strengthand measuring the errors, and b) the baseband operation starting pointto start operation from a high baseband power level which is higher thana low baseband power level used when detecting the electric fieldstrength and measuring the errors, wherein while receiving the pluralityof time division multiplexed programs other than the selected program,the radio frequency operation starting point and the baseband operationstarting point are varied in accordance with a) and b) in response tothe detected electrical field strength being above a predeterminedelectric field threshold and the measured errors in the received datapackets being above a predetermined error threshold.
 2. The digitalbroadcasting receiving apparatus according to claim 1, wherein aparameter switch timing generating circuit controls a switch in responseto the detected electrical field strength, wherein the switch switchesbetween a vertically polarized antenna and a horizontally polarizedantenna.
 3. The digital broadcasting receiving apparatus according toclaim 1, including an analog to digital converter, an output signal ofthe baseband variable gain circuit is an input signal to the analog todigital converter, wherein the radio frequency operation starting pointand the baseband operation starting point are varied to ensure that theinput signal to the analog to digital converter maintains a constantlevel.